Poj 1201 difference constraint + SPFA

/*s[b+1]-s[a]>=cs[i+1]-s[i]>=0s[i]-s[i+1]>=-1*/#include<iostream>#include<cstdio>#include<cstring>#include<algorithm>#include<queue>using namespace std;#define maxn 50005struct node{    int v,w,next;}edge[maxn<<2];int id,end,st;int a,b,c,n;int head[maxn];bool in[maxn];int d[maxn];void init(){    memset(head,-1,sizeof(head));    end=id=0;    st=0x3f3f3f3f;}void addedge(int a,int b,int c){    edge[id].v=b;    edge[id].w=c;    edge[id].next=head[a];    head[a]=id++;}void SPFA(){    queue<int> Q;    memset(in,0,sizeof(in));    memset(d,-0x3f,sizeof(int)*(end+5));    Q.push(0);    in[0]=1;    d[0]=0;    int tmp;    while(!Q.empty())    {        tmp=Q.front();Q.pop();        in[tmp]=0;        for(int i=head[tmp];i!=-1;i=edge[i].next)        {            if(d[edge[i].v]<d[tmp]+edge[i].w)            {                d[edge[i].v]=d[tmp]+edge[i].w;                if(!in[edge[i].v])                {                    in[edge[i].v]=1;                    Q.push(edge[i].v);                }            }        }    }}int main(){    while(scanf("%d",&n)==1)    {        init();        for(int i=1;i<=n;i++)        {            scanf("%d%d%d",&a,&b,&c);            addedge(a,b+1,c);            end=max(end,b+1);        }        for(int i=0;i<end;i++)        {            addedge(i,i+1,0);            addedge(i+1,i,-1);        }        SPFA();        printf("%d\n",d[end]);    }    return 0;}